1. Technical Field
The present invention generally relates to the field of metrology tools, and, more particularly, to metrology tool stage design.
2. Discussion of Related Art
Metrology tool stages allow respective positioning of wafers and optics to enable measurement of wafer areas. Typical metrology tool stage configurations suffer from different limitations such as leaving a large tool footprint, ineffectively using the stage travel, and are limited in the stage acceleration due to large moving masses and stack of the axes. These configurations have other limitations in stage stiffness due to large axis strokes, in stage flatness at wafer level, and in counter-mass implementation, thus most of the stage impact is transferred directly to the environment. As wafers increase in size, these problems are increased and compounded.
FIG. 1 is a high level schematic illustration of a metrology tool stage configuration 90 according to the prior art. In the prior art, movements of wafer 75 are conducted in two linear and perpendicular directions, denoted in FIG. 1 by X and Y. Wafer 75 is moved into a position in which the measured wafer area is under the central and stationary optics 70. Wafer movements X, Y are controlled by a guiding system 91 comprising external movement guides and attachment means to wafer 75. A footprint 94 is the area required to accommodate all possible wafer movements (wafer travel). It is noted that in the prior art, the stage system uses beyond footprint 94 also a circumference of footprint 94 which occupies guiding system 91. Furthermore, the immediate vicinity of footprint 94, which includes areas 95 of the square bounding footprint 94 and having sides with the diameter of footprint 94, likewise cannot be used for any purposes (e.g., supporting optics 70) in order not to obstruct the operation and free movement of guiding system 91, and is hence a wasted stage space.
As wafer sizes increase, stage travel and moving mass increase dramatically and together, with demanded increase in acceleration, require unrealistically high power motors which generate a lot of heat and again increase the moving mass. Short move and settle time require extremely high mechanical stiffness of stage axes, which again leads to increasing the moving mass. These considerations are not conducive to providing a small tool foot print. The typical approach of orthogonal XY stage is very inefficient in term of wafer coverage to stage foot print ratio, as shown in FIG. 1.
It is noted that typical configurations with stationary optics are configured to move along perpendicular axes X, Y and not along radial and rotation axis, while typical configurations with rotatable wafers also have rotatable and/or linearly movable optics. The former has the disadvantage of a relatively large footprint and unused footprint periphery (occupied by guiding systems and left free to enable guiding system operation), while the latter is complex and slow in the operation of the moving optics and suffers inaccuracies due to the movements of the optics.
Therefore, there is a long-felt need for an improved metrology tool stage configuration that allows a small footprint associated with a tool, and fast in the operation of the moving optics without sacrificing accuracy.